This invention pertains to forced-circulation heat transfer devices of the flat-plate type or embossed-sheet type. Dual circuit heat transfer systems are typically employed where different flow components of a system must be maintained in chemical or pressure isolation, or where redundancy of a heat transfer system is required. The latter situation is encountered in fusion reactor design, especially a forced-circulation-cooled first wall of a reactor facing a plasma. In such applications, the mass of the wall in contact with the plasma must be kept to a minimum to reduce neutron absorption and thereby increase the breeding of tritium as fuel, since neutron multiplier and lithium lithium-containing materials are typically located immediately behind the first wall. Further, the redundancy provided must allow for uniform cooling over all portions of the first wall during and after the plasma "burn" time period, so as to eliminate local hot spots occurring in out-of-service cooling circuits.
Embossed sheet-panel construction offers several advantages for fusion reactor application. In this type of construction, two sheets, one or both of which are embossed or corrugated, are joined together to form a series of coolant passageways. The sheets are typically joined by a continuous resistance weld, a method which causes minimal impact on the radiation damage resistance of the sheet material, in that the micro-structure of the sheet material is not markedly changed in the weld area. However, embossed-sheet panel constructions available today having more than one coolant circuit are not suitable for use as the redundant cooling system for nuclear reactors as described above. The multiple circuits in such constructions have inlet and outlet manifolds which are common to all circuits in a given panel, and thus do not offer coolant circuit redundancy since an entire panel must be placed out-of-service in order to place any of the multiple channels in an out-of-service condition. This would result in damage to the out-of-service panel when used in a high heat load application or when cooling down an irradiated panel after ending a plasma burn.
Other constructions available today use three full sheets of panel material, with coolant channels formed on both sides of a flat middle sheet by the two other embossed sheets. These constructions offer redundancy adequate for cooldown of an irradiated panel, but do not provide adequate panel cooling if the circuit on the high heat load side (plasma-facing side) is placed in an out-of-service condition. Also, such constructions require three or more full sheets of panel material and two full layers of coolant channels, which is unsuitable for use in a cooling member exposed to a plasma of a nuclear reactor, since the overall skin thickness of the cooling member causes high neutron absorption rates, and also if the coolant is water, the neutron energies are moderated (reduced) to an undsirable level.